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I've read that a triple stage combustion light gas gun can fire for a muzzle velocity of 12km/s. That's faster than the escape velocity needed to escape earth's gravitational influence.Thus, im going for this speed value.

Suppose a 155mm CLGG fires a tungsten projectile at a target below at a speed of 12km/s, will it be effective enough to act as an artillery shell fired from orbit but it's area effect relies solely on speed and kinetic energy? Rods from god would take 12-15 minutes to reach ground target from orbit, and that's at a starting velocity even lower than 8km/s because you need to de-orbit the rod first.

The main goal is to significantly cut the travel time of a kinetic energy weapon from orbit to ground, by aiming it downwards, and fire at a ridiculous velocity, and to also provide an orbital strike package at a tactical level, where any soldier in my setting, can simply "telepathically" tap into available orbital strike CLGGs using their neural interface, ridding them of much of the wasteful seconds tapping into their devices that could have been put to focus in ground fighting. There are HGVs dropped from orbit to achieve the orbital strike role but that'll take 12-15 minutes depending on it's trajectory and flight path. Will a 155mm CLGG in orbit firing a tungsten projectile downwards into the planet at 12km/s be effective/destructive enough at a tactical level?

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    $\begingroup$ Note that you need a vast number of orbital platforms to always have one "overhead" for all points on Earth where fighting may be occurring. ("Huge" being thousands or tens of thousands, like Starlink.) If you are waiting for one to get into the right window then the delay is probably much the same as for a Thor shot (or rods from god, as you're calling them). Even if you have an orbital platform within 5 minutes at any time, on average you will get faster time-on-target with a ground-based battery of 155's in support. $\endgroup$ Commented Dec 20, 2023 at 14:47
  • $\begingroup$ What do you think about long-endurance loitering munitions at 18-20k feet above? Assuming 50 hours of endurance, since i don't think they can just tap into the 155s using their neural interface that easily as compared to an AI-powered autonomous system (such as loitering munitions) that will answer to the call almost immediately. $\endgroup$
    – Vexorr
    Commented Dec 20, 2023 at 16:17
  • $\begingroup$ I suggest that you ask a separate question about that idea, but note that meaningful answers will require a lot of background on enemy anti-air capability etc. Also note that we look at one problem at a time, so the neural interface and what communications system it is linked to are separate issues that need to be further separate questions if you really want to dive into the intricacies of a neural user interface and/or supporting battlefield comms network. (Check existing questions for whether they answer your problem first, please, before posting a new question.) $\endgroup$ Commented Dec 20, 2023 at 20:37
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    $\begingroup$ A military with the capability of putting thousands of orbital bombardment satellites in orbit has much simpler and cheaper methods of providing directed fire/artillery. Loitering munitions or just conventional artillery systems that are very far away could do the same but cheaper and faster probably. Also, I'm skeptical that a kinetic orbital strike is worth it in any scenario. The expense to ship mass to LEO is just enormous, so unless you are doing bombardment by eg. redirected space rocks, I don't think it's worth it. Maybe directed energy satellites, but again, only maybe. $\endgroup$
    – Dragongeek
    Commented Dec 20, 2023 at 21:00
  • $\begingroup$ The "neural net" is just a distraction from the question. All it does is generate fire orders ("attack these coordinates at this time") slightly faster than a lieutenant with a compass and map. The system that services those missions doesn't need to know, and probably shouldn't care, about the system that generates them. $\endgroup$
    – Cadence
    Commented Dec 21, 2023 at 0:50

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Such an orbital CLGG would need to be at an altitude of at least 200 km. At 12kps, the projectile would take about 16.7 seconds to travel from the firing satellite. Traveling straight down, the projectile would accelerate by a negligible 164 m/s, discounting atmospheric effects.

A properly designed long-rod penetrator should be capable of destroying most battlefield targets... if it hits. The problem with getting the projectile to hit is that as it travels through the atmosphere, it would be enclosed in an opaque mass of plasma as its tip ablates from impact with countless molecules of air. The plasma from atmospheric reentry has been shown to put the descending object within it out of effective contact via radio signals, and obscures the object from optical observation and by extension, optical communication.

This would mean that the projectile would effectively be a dumb-fired shot. It would rely upon the initial aim of the launching platform and the accuracy of the instructions from the forward observer. If the intended target was mobile, in those 16-odd seconds, it could deviate significantly from its projected course, which would cause this hyper-velocity projectile to strike an innocuous patch of soil rather than an enemy asset.

While it would take Rods from the Gods longer to de-orbit, and they would not hit at such a high velocity, RftGs have the advantage that they can be deployed in large numbers, and are therefore capable of saturation bombardment of an area, while orbiting a CLGG and its ammunition would be an expensive proposition, and CLGGs would therefore be available in limited quantities, and would be unlikely to be able to perform the necessary saturation bombardment of the area.

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  • $\begingroup$ 16 seconds is enough to hit a tank or armor column though (especially with the explosion-like impact damaging a somewhat wide radius) $\endgroup$
    – Hobbamok
    Commented Dec 21, 2023 at 16:14
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Frame Challenge - This weapons system will not work

155mm? Your projectile burned up in the Atmosphere before it even got close to making an impact.

For reference - The NASA estimate of how large a Meteorite has to be to traverse through the atmosphere and hit the ground is 5 Meters in diameter - however they give another answer - that anything less then 25 meters in diameter is unlikely to impact the earths surface and cause damage.

Now - you might counter 'Ah, but my Weapons system is Tungsten! the Meteorites aren't made of Tungsten!' - and you would be correct, Meterorites are primarily made from Silicates - which have fantastic thermal properties - including a boiling point around that of Tungstens melting point.

Once your projectile hits the atmosphere - it will start to get very toasty very quickly and even if it doesn't vaporize, it will start to melt, which will deform the projectile, which will increase the aerodynamic drag, causing more friction, causing it to go off-course etc. etc.

Even if you could put a protective shield around the projectile with some super-high melting material (Hafnium Carbonitride) - I still think this would melt from the friction - even if it doesn't outright melt, if it gets hot enough to start plastic deformation - you've still got the Drag/Accuracy problem.

In short - you need a much larger projectile to traverse the atmosphere and a means of having a sacrificial series of layers that will absorb the heat and break away without altering the course of the projectile - for that it will need to be much larger than 155mm.

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  • $\begingroup$ Note that an artillery shell is shaped in a way that creates less drag relative to mass, and is made of more durable materials. Obviously a 155mm shell would still vaporize on atmospheric entry but there are mitigating factors. $\endgroup$
    – KEY_ABRADE
    Commented Dec 21, 2023 at 0:42
  • $\begingroup$ The drag problem alone would be prohibitive if 155mm refers to its length. As a rule of thumb, from momentum considerations, regardless of speed your projectile needs a mass per frontal area at least as large as the mass of air you want it to punch through. It needs to punch through about 1 kg per cm^2 (a 1 cm^2 column of air from sea level to space masses about 1 kg). A 155mm-long rod of tungsten masses only 0.3 kg/cm^2. So it will stop. $\endgroup$
    – causative
    Commented Dec 22, 2023 at 1:30
  • $\begingroup$ 155 mm refers to diameter, it's a standard artillery size - approx 6 inches IIRC $\endgroup$ Commented Dec 22, 2023 at 2:14
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This doesn't work for a multitude of reasons. One is that a multi-stage CLGG has a terrible projectile-to-gun mass ratio. Yes, you might get 12 km/s - but you'll be launching a 1-gram projectile out of a 1-ton gun. Good for scientific experiments, useless for anything else.

Orbital projectiles are already almost too fast to survive reentry. A 1-ton tungsten rod at 8 km/s can do it. A 1-gram pellet can't.

If you need instantaneous strikes from orbit, you're much, much better off using pure energy weapons - lasers, solar mirrors, possibly other forms of radiation.

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Maybe possible, but think more of something like a hypersonic missile. These can survive 8km/s in atmosphere. I've heard that they can use just the kinetic momentum alone to cause destruction. But I think you would have to come up with something that is a cross between a hypersonic missile an artillery round. Even the long range artillery rounds have steering, I've heard that they can achieve 100km ranges with newer tech.

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